Method of treating silica gel



May 28, 1946.

A. S. BEHRMAN METHOD OF TREATING SILICA GEL 2 Sheets-Sheet 1 Filed Aug.14, 1942 INVENTOR dbra/zam 92W fie/zrmm y A. s. BEHRMAN 2,400,907

METHOD OF TREATiNG SILICA GEL Filed'Aug. 14, 1942 2 Sheets-Sheet 2' Q 7INVENTOR.

d/U/ZQWZ fimgqfls/zrmm Patented May 28, 1946 iTED STATES METHOD orTREATING slLroa GEL Abraham Sidney Behrman, Chicago, Ill., assignor toInfilco Incorporated, Chicago, 111., a corporation of DelawareApplication August 1 4, 1942, Serial No. 454,875

4 Claims.

This invention relates to the manufacture of siliceous gels and hasreference more particularly to a method and apparatus for thepreparation of siliceous gels used as catalysts, catalyst carriers,adsorbents and for other purposes.

In my copending application, Serial No. 371,000, filed December 20,1940, now issued as Patent No. 2,358,202, I have described a process ofproducing certain types of low density siliceous gels in which the castgel is subjected to hydraulic or other. pressure, to squeeze out excessliquid from the gel. This pressed gel is then placed in an autoclave andsubjected to a steam pressure of freshly precipitated and pressedsiliceous gel.

Another object of the invention is to provide a method of continuouslysteaming and drying silica gel which will result in lowered cost ofproduction.

A further object of the invention is to reduce the large lumps of gelprior to treatment and to produce a minimum of fines.

A still further object of the invention is to provide an apparatus forefficiently carrying out the above method; also to-improve methods ofand apparatus for preparing siliceous gels and catalytic compositions inother respects hereinafter specified and claimed.

Reference is to be had to the accompanying drawings forming a part ofthis specification, in

which Fig. 1 is a diagrammatic, fragmentary. sectional elevation of anapparatus suitable for carrying out the method,

Fig. 2 is a fragmentary plan view of the apparatus, Fig. 3 is an endelevation of th apparatus, and Fig. 4 is a side sectional elevation of amodified form of apparatus.

Referring to the drawings by numerals. a drying chamber l0, preferablybut not necessarily of the steam coil and moving hot air type, isprovided with an endless and foraminous apron or belt II which is oftenmade of woven wire. This belt (not shown) at the opposite end of thedrying chamber l0. Silica gel is generally precipitated by mixing twosolutions, such as sodium silicate and a mineral acid. If desired, acatalytic agent may be added to the solution and the gel is allowed toset and is partially de-watered by hydraulic or other pressing tosqueeze out excess water. The moist and pressed siliceous gel I3 is thendeposited onto the foraminous belt It. Thisgel contains, dissolved inthe water with which it is saturated, a substantial amount of solublesalts resulting from the gel forming reactions, and it is sometimesdesirable that these salts be removed, since otherwise they are apt tointerfere with the use of the gel composition as acatalyst.

Mounted on the front end of the drying chamber I0 is a steaming chamberH which has an open bottom It spaced somewhat above the foraminous beltlit The chamber I4 has a front wall It and a rear wall IT. The chamberl4 may be conveniently formed of metal with closed ends. A steam pipe l8leading from a source of steam, such as a boiler, is provided withdownwardly directed Jets l9 so that steam impinges directly on a layer20 of the siliceous composition l3 which is leveled off by the frontchamber wall IS. The excess of the composition l3 backs up to form aridge 22 behind the front chamber wall It which thus forms a seal toprevent undue leakage of steam from the chamber It. When the steam jetsl9 travel through the cold composition layer 20, water of condensationis formed from the steam, and this water serves to dissolveout solublesalts from the silica gel composition, thus aiding considerably inpurifying the silica gel.

Water of condensation is collected in a catch basin 23 having a drainpipe II. The steam suddenly heats the silica gel so as to lower thedensity of the dried catalytic composition, form a fibrous structure,and thus improve its catalytic characteristics. condensation has atendency to flow down the wire belt H by capillary attraction and forman objectionable pool of water on the floor 25. This condition isaggravated because the wire belt ll travels upwardly on a slope. Thiswater of condensation contains dissolved salts which are corrosive onthe conveyor chains and wire belts. In order to avoid this condition, Iprovide an air pipe 21 which leads from the front of dryin chamber III.A plurality of branch pipes 28 lead from the pipe 21 and direct hot airblown by fans (not shown) in the chamber to, into the top of movesaround a p lley l2 nd a second pull y steam chamber II. This hot airserves to blow I have found that the water of the Water of condensationthrough the belt ll into catch basin 23 and thus prevent the water fromflowing down the belt H and forming a pool of water on the floor. Thishot air and steam mixture passing through the layer 20 also serves tofree the silica gel from impurities and excess water. A slab of heatinsulation 30 is provided on the front wall l6 to prevent thecomposition inridge 22 from becoming overheated.

In the modified form of apparatus shown in Fig. 4, the hydraulicallypressed siliceous gel containing about 79% moisture is delivered by aconveyor belt 33 to a hopper 34 which is provided near its bottom outletwith a pair of spaced apart driven crushing rolls which serve to breakup i the large lumpsof gel in hopper 34 and deliver the sized gel to ascreen belt 36. The fine material in the gel in hopper 34 falls throughand the large lumps are crushed to small sizes depending on the spacebetween rolls 35. The wire belt passes through a space 38 beneath afront wall 39 of an elongated steaming chamber 40, said front wallserving to level ad the gel to a uniformly thick layer on said belt 36.Steam is introduced into chamber 40 through pipe 4| controlled by valve42.

The steam passes through the layer of gel 43 on belt 36 and condensesonthe-gel, thus suddenly raising the temperature of the gel. This suddenapplication of heat to the gel produces some internal and unknown changein the gel to lower the apparent density of the dried gel to 30-35 lbs.per cubic foot. The steam treatment or cooking effect is obviously verybrief as the steaming chamber is relatively small. and is therefore tobe clearly distinguished from my above mentioned copending applicationin which the pressed hydrogel is subjected to autoclaving for prolongedperiods. Without the steam treatment of the gel. the dried gel wouldhave an apparent density of 45 lbs. per cubic foot. The water .ofcondensation from the steam drains through the wire belt 36 into acatchbasin 45 provided with a drain pipe 46. The gel in the steaming chamber40 suffers a slight decrease in weightdue to theaction of the steam.

The steamed gel 43 emerges from steam chamber 40 and slides down chute48 on to drier wire belt 49 which serves to retard the fall of the lumpsof gel and reduce the amout of waste gel fines produced. The gel ondrier wire belt 49 passes under the front wall of a drier chamber 50,said wall serving to level off the gel to a uniform gel'layer BI andalso form an airs'eal for the chamber 50. The gel is dried in thechamber 60 and is discharged at the delivery end of drier 50 for furthertreatment. 4

The use of the separate steaming belt 36 has the advantage that thespeed of said belt 36 may be varied relative to the speed of belt, 69thus providing a greater flexibility in operation and steaming time. Thesteaming belt 36 can also be given ananti-corrosive protective coatingwhich-will reduce the corrosive action of the steam treatment on themetals of the belt 36.

I would state in conclusion that, while the illustrated examplesconstitute practical embodiments of my invention, I do not wish to limitmyself precisely to these details, since manifestly. the same may beconsiderably varied without departing from the spirit of the inventionas defined in the appended claims.

Having thus described my invention, I claim as new and. desire to secureby Letters Patent:

1. The method of treating a freshly pressed silica hydrogel containing asubstantial quantity of integral salt water solution, which comprisessteaming said hydrogel at substantially atmospheric pressure for aperiod sufflcient only to rapidly heat said hydrogel to about theboiling point of water, immediately terminating such heating, andthereafter drying said hydrogel.

2. The method of treating a silica hydrogel containing a substantialquantity of integral salt water solution, which comprises steaming saidhydrogel .at substantially atmospheric pressure sumciently to rapidlyraise the temperature of the hydrogel to about the boiling point ofwater, immediately terminating such steaming, and drying said hydrogel.

3. The method of treating a freshly pressed silica hydrogel containingabout 79 per cent moisture which comprises steaming said hydrogel atsubstantially atmospheric pressure for a period suflicient only to-heatthe hydrogel to about the boiling point of water, and immediately dryingthe hydrogel.

4. The method of treating a silica hydrogel which comprises pressingsaid hydrogel sufllciently to reduce the moisture content of saidhydrogel to the order of about '79 per cent of the total weight of thehydrogel. forthwith subjecting said hydrogel to steam at atmosphericpressure for a period suflicient only to rapidly heat said hydrogel toabout the boiling point of water, and then drying said hydrogel.

ABRAHAM SIDNEY BEHRMAN.

